The determination of carcinoembryonic antigen (hereinafter CEA) is well documented in the art. It is likewise well established that certain non-specific interfering substances present in the sample to be tested must be substantially removed or neutralized in some manner in order for the determination to be accurate and sensitive.
There are a number of procedures known in the art by which potentially interfering substances present in a sample of biological fluid, e.g., serum or plasma, can be removed or neutralized before testing for CEA. It is clearly an advantage to simplify the manipulations required to remove such interfering substances in a given assay in terms of time, cost and relative ease in conducting the test.
More particularly, in the determination of CEA as taught in Freedman et al., U.S. Pat. No. 3,663,684, tissue containing CEA is initially treated with a glycoprotein solvent in which CEA is soluble. Examples of such solvents include perchloric acid, trichloroacetic acid, phosphotungstic acid, and the like. The purpose of treating the tissue with the glycoprotein solvent is to remove precipitable normal proteins and interfering antigenic materials. The precipitated interfering protein material is thereafter removed from the sample by centrifugation.
More recently, Hirai, Cancer Research 37, 2267-2274, July 1977, and Kim, et al., Clinical Chemistry 25, No. 5, 773-776, 1979, have reported a method of determining CEA utilizing a preparative heat treatment in place of the extraction with a glycoprotein solvent, such as perchloric acid. The latter publication describes this method of preparation of sample to remove interfering substances as buffering the sample to a pH of 4.8 to 5.0 with acetate buffer and heating it to between 70.degree. C. and 80.degree. C. for from 10 to 20 minutes. This heat treatment in the presence of a high ionic strength buffer at acid pH., e.g., heat denatures the interfering proteins which coagulate. It is, therefore, essential that the sample be centrifuged to remove the coagulated material. This procedure is disadvantageous in that CEA present in the sample may become entrapped in the coagulated material and thereby removed from the sample to be tested, thereby detracting from the accuracy of the subsequent determination.
In accordance with the present invention, a method is disclosed for the preparation of a sample of human serum or plasma for assay for determination of CEA which is more rapid, easier and less expensive than the preparative methods known in the art and which is advantageous in that the sample need not be centrifuged.